1. Field of the Invention
The present invention relates to an electroacoustic conversion film web which is processed to be used as an electroacoustic conversion film used for an acoustic device such as a speaker or a microphone, an electroacoustic conversion film, and manufacturing methods thereof.
2. Description of the Related Art
In response to thinning of displays such as liquid crystal displays and organic electroluminescence (EL) displays, speakers used in such thin displays are also required to be lighter and thinner. As such a lightweight and thin speaker, it is considered to adopt a sheet-like piezoelectric film having a property that stretches and contracts in response to an applied voltage.
For example, in JP2008-294493A, it is described that a piezoelectric film obtained by performing polarization processing with respect to a monoaxially stretched film of polyvinylidene fluoride (PVDF) at a high voltage is used.
In order to adopt the piezoelectric film as a speaker, it is necessary that a stretching and contracting movement along a film surface is converted into a vibration of the film surface. This conversion from the stretching and contracting movement into the vibration is attained by holding the periphery of the piezoelectric film in a bent state, and thus the piezoelectric film is able to function as a speaker.
Here, the present applicants suggested, as a piezoelectric film capable of being used for a thin speaker, an electroacoustic conversion film including a polymer composite piezoelectric body in which piezoelectric body particles are dispersed in a viscoelastic matrix formed of a polymer material having viscoelasticity at a normal temperature, thin film electrodes formed on both surfaces of the polymer composite piezoelectric body, and protective layers formed on the surfaces of the thin film electrodes, which is disclosed in JP2014-14063A.
In such a piezoelectric film, two thin film electrodes forming an electrode pair for applying a voltage to a piezoelectric layer are formed on both surfaces of the piezoelectric layer that stretches and contracts in response to an applied voltage, and wires need to be connected to the two thin film electrodes.
On the other hand, the piezoelectric film used as a thin speaker also needs to be thinner from viewpoints of not only thinning of the speaker but also responsiveness and widening of a reproducible band. However, in a thin electrode layer such as a vapor-deposited film, it is difficult to connect wires by soldering or the like.
In addition, connection of wires to the thin film electrodes needs to be performed while insulation between the thin film electrodes on both surfaces of the piezoelectric layer is ensured. However, the connection of wires is not easy because the thickness of the piezoelectric layer is as thin as approximately tens of vim.
Regarding this, in JP2014-209724A, the applicant proposed an electroacoustic conversion film having a configuration in which thin film electrodes and protective layers have electrode lead-out portions protruding in a convex shape, in the outer portions of a piezoelectric layer in a surface direction. With this configuration, electrodes can be drawn from the thin film electrodes and connection of wires by soldering can be easily performed. Furthermore, drawing of the electrodes can be performed while insulation between the thin film electrodes on both surfaces is ensured.